| Schwinger's variational principle (J. Schwinger's lecture notes at Harvard University, 1947) is formulated for electronion (atom) collision using the coulomb (free particle) Green's function. The theory is applied to a screened coulomb potential as well as e('-) - He('+) and e('-) - H to obtain analytic distorted waves, phase shifts, and quantum defects for energies near the ionization threshold. A numerical technique of calculating the phase shifts and wave functions is also outlined. |
